The present invention relates to an umbilical for transmission of fluids and electric current/signals between the sea surface and equipment located on the sea bed, in particular in deep waters, comprising a number of pipes and electric conductors/wires collected in a bundle, a filler material arranged at least partly around and between the pipes and conductors/wires, and a protective sheath enclosing the pipes, conductors/wires and filler material.
Umbilicals of this type are constructed as a composed structure which is able to transfer hydraulic liquids, chemicals, fluids, electric and optical signals and electric power between equipment on the sea bed and on the sea surface. An early version of such umbilicals is known from WO 93/17176. Typical for this umbilical is that most of the load transfer takes place in a centrally located steel pipe of substantial dimension. Further examples of prior art are disclosed in GB 2 326 177 A and GB 2 326 758 A, all having the same assignee as the present invention.
An International patent application no. PCT/NO05/00215 related to a power umbilical is simultaneously filed.
The above mentioned heavy section steel pipes ad substantial weight to the umbilical due to their own weight. The pipes need to have such large dimensions just because they act as load carrying elements, and not because the transported medium requires this. Thus the sea depth to which the umbilical having the traditional construction can be used is limited.
Instantly it appears as steel rope could be used as load carrying elements. This, however, do not solve the problem in considerable extent. Steel rope also ad substantial weight and in combination with heavy pipes, one do not reach large depths before the umbilical achieves yield stresses and are tom off due to its own weight.
Substantial efforts and resources have been used in order to find a solution on how to be able to use these umbilicals down to the sea bed at real large sea depths, such as 2500 meters and more.
This is now solved by combining a technology that is developed by the assignee of the present invention, viz. the technology that is used for tension legs of floating platforms. See for example WO 02/057560 A1.